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Default Ground Loop? (Ground Loop Isolators Have No Effect)

I have a laptop in my trunk which I'm using as an MP3 player. Up until
recently I used a cassette adaptor to pipe the sound into my 2000
Passat's factory head unit. I decided to upgrade the sound quality a
bit, and bought a PIE VW-AUX (a device which converts the unused CD
Changer connector in my trunk into an auxiliary input) adaptor and now
have the audio from the laptop running through it to the head unit.

Everything works like a charm as long as the laptop is running off its
own internal battery. If I select CD1 on the head unit, I can hear
nice clean(ish) audio from the laptop.

When I have the laptop connected to the power inverter (plugged into
the cigarette lighter socket in the trunk), though, I get this really
loud buzzing/humming sound coming through the speakers (lound enough to
almost drown out the music completely). It doesn't matter whether the
laptop is on or not - as long as its plugged into the car battery
through the inverter, I get a loud humming sound when the CD changer is
selected on the head unit. About 5% of the time, the humming sound
might go away for a little while, but always comes back again.

I did some research, and it sounds like I have what's called a "ground
loop" problem. However, I've tried two different ground loop isolators
(one was made by a company called Stingray, and the other was the PIE
EIS-ILNO, which is supposed to be both a ground loop isolator and noise
filter) and neither one has had any effect.

I've tried a different power inverter, but the humming sound is still
there. If I'm in the garage and plug the laptop to house AC current
the humming is gone (although this isn't a viable solution for the
obvious reason ;-)

Is this a ground loop problem, and if so why aren't the ground loop
isolators making any difference?

If not, what is it and how do I fix it?

Is it "safe" to leave things in this situation? At the moment, I have
the inverter on to charge the laptop battery only when I'm NOT
listening to music through it and switch the inverter off when I'm
listening to music. However, the radio is on when the laptop is
charging so whatever is causing the humming is still coming in through
the CD input even though I'm listening to the radio. Is this harmful?
Thanks!

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imij
 
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I think you have accurately identified the problem, but it looks like
the only solution i have is the one you have tried.


http://www.epanorama.net/documents/g...oop/index.html

here is a good explanination of ground loops and ways to fix

according to this site, ground loops could cause damage to the system.

according to the site "A ground loop in the power or video signal
occurs when some components in the same system are receiving its power
from a different ground than other components, or the ground potential
between two pieces of equipment is not identical"

my personal suggestions: (not based on experience, only on information
from the above site.)

OBJECTIVE: Eliminate ground loops
Ground loops are caused by the resistance between the grounds of two
electrical items not equaling zero. So, how do you make the resistance
between the two grounds equal zero?

Solution.
1 move the grounds closer together(inverter ground closer to wherever
the audio ground). Less distance = less resistance. Methods for
execution are : Try hardwiring the inverter to your car instead of
using the cigarett adapter (remember thicker wire means less
resistance, but at some point the effects of larger wire become
insignificant. There are charts that give the resistance of a certain
gauge wire over a specified distance. the relationships are also not
linear.).

this may just be a waste of time.

you might want to barrow somone else's inverter and test the effects as
well. i am not implying that there is anything wrong with the
inverter, but different circuitry might have a different effect on the
system.

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Kevin McMurtrie
 
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In article .com,
wrote:

I have a laptop in my trunk which I'm using as an MP3 player. Up until
recently I used a cassette adaptor to pipe the sound into my 2000
Passat's factory head unit. I decided to upgrade the sound quality a
bit, and bought a PIE VW-AUX (a device which converts the unused CD
Changer connector in my trunk into an auxiliary input) adaptor and now
have the audio from the laptop running through it to the head unit.

Everything works like a charm as long as the laptop is running off its
own internal battery. If I select CD1 on the head unit, I can hear
nice clean(ish) audio from the laptop.

When I have the laptop connected to the power inverter (plugged into
the cigarette lighter socket in the trunk), though, I get this really
loud buzzing/humming sound coming through the speakers (lound enough to
almost drown out the music completely). It doesn't matter whether the
laptop is on or not - as long as its plugged into the car battery
through the inverter, I get a loud humming sound when the CD changer is
selected on the head unit. About 5% of the time, the humming sound
might go away for a little while, but always comes back again.

I did some research, and it sounds like I have what's called a "ground
loop" problem. However, I've tried two different ground loop isolators
(one was made by a company called Stingray, and the other was the PIE
EIS-ILNO, which is supposed to be both a ground loop isolator and noise
filter) and neither one has had any effect.

I've tried a different power inverter, but the humming sound is still
there. If I'm in the garage and plug the laptop to house AC current
the humming is gone (although this isn't a viable solution for the
obvious reason ;-)

Is this a ground loop problem, and if so why aren't the ground loop
isolators making any difference?

If not, what is it and how do I fix it?

Is it "safe" to leave things in this situation? At the moment, I have
the inverter on to charge the laptop battery only when I'm NOT
listening to music through it and switch the inverter off when I'm
listening to music. However, the radio is on when the laptop is
charging so whatever is causing the humming is still coming in through
the CD input even though I'm listening to the radio. Is this harmful?
Thanks!


You probably have one of the many piece-of-crap inverters that have a
live neutral. An audio ground loop eliminator is meant to block a volt
or two of ripple, not a spiky 60V square wave.

There are solutions -

1) Find a quality, true sine wave, AC inverter with an isolated output.

2) Use the piece-of-crap AC inverter, ground the laptop's chassis to
your car's chassis, and use an audio ground loop eliminator. Some
appliances aren't safe with a live neutral so there's a slight chance
that your laptop's power adaptor will eventually burn out.

3) Use an inexpensive common ground DC-DC inverter with an audio ground
loop eliminator. RatShack and some other places sell them. Powering
the laptop with a single inverter will save about 1 amp of car battery
drain too.

4) Use a more expensive isolated DC-DC inverter to power your laptop.
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Kevin McMurtrie wrote:
In article .com,
wrote:

I have a laptop in my trunk which I'm using as an MP3 player. Up

until
recently I used a cassette adaptor to pipe the sound into my 2000
Passat's factory head unit. I decided to upgrade the sound quality

a
bit, and bought a PIE VW-AUX (a device which converts the unused CD
Changer connector in my trunk into an auxiliary input) adaptor and

now
have the audio from the laptop running through it to the head unit.

Everything works like a charm as long as the laptop is running off

its
own internal battery. If I select CD1 on the head unit, I can hear
nice clean(ish) audio from the laptop.

When I have the laptop connected to the power inverter (plugged

into
the cigarette lighter socket in the trunk), though, I get this

really
loud buzzing/humming sound coming through the speakers (lound

enough to
almost drown out the music completely). It doesn't matter whether

the
laptop is on or not - as long as its plugged into the car battery
through the inverter, I get a loud humming sound when the CD

changer is
selected on the head unit. About 5% of the time, the humming sound
might go away for a little while, but always comes back again.
[snip]


You probably have one of the many piece-of-crap inverters that have a


live neutral. An audio ground loop eliminator is meant to block a

volt
or two of ripple, not a spiky 60V square wave.

There are solutions -

1) Find a quality, true sine wave, AC inverter with an isolated

output.
[snip]


I thought I'd post a follow-up with the "final solution". Kevin was
correct: the problem was with the power inverters. True sine wave
inverters are massively expensive, but there's a cheaper (and totally
adequate solution).

While doing research, I came across a product made by a company named
Vector. They make a line of inverters (MAXX SST) that advertise ("New
Noise-Free Technology"). I bought the 225 WATT model (TVEC034) at the
local Target for less than $30 and it has almost completely solved my
electrical noise problem (if I gun the volume up to the max I can hear
a very soft buzzing, but I'd never have the volume anywhere near that
high when listening to music).

My "only" complaint about the unit is that it's cooling fan is pretty
loud (loud enough that I can hear it in the trunk of my Passat sedan
when I'm sitting at a stop light), but I can live with that! :-)

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